Re: [PATCH 0/2] setgid hardening

[Willy Tarreau]

On Wed, Jan 25, 2017 at 01:06:50PM -0800, Andy Lutomirski wrote:
> The kernel has some dangerous behavior involving the creation and
> modification of setgid executables.  These issues aren't kernel
> security bugs per se, but they have been used to turn various
> filesystem permission oddities into reliably privilege escalation
> exploits.
> 
> See http://www.halfdog.net/Security/2015/SetgidDirectoryPrivilegeEscalation/
> for a nice writeup.
> 
> Let's fix them for real.

BTW I like this. I vaguely remember having played with this when I
was a student 2 decades ago on a system where /var/spool/mail was
3777 (yes, setgid+sticky) and the mail files were 660. You could
deposit a shell there, then execute it with mail's permissions and
access any mailbox. That was quite odd as a design choice. The
impacts are often limited unless you find other ways to escalate
but generally it's not really clean.

Willy